test(screenshots, spawn): require exact major gtk/gdk versions (#3460)

tests/test-screenshot.lua

@@ -4,9 +4,9 @@
 local wibox = require("wibox")
 local spawn = require("awful.spawn")
 local gsurface = require("gears.surface")
-local lgi = require 'lgi'
+local lgi = require('lgi')
 local cairo = lgi.cairo
-local gdk = lgi.Gdk
+local gdk = lgi.require('Gdk', '3.0')
 
 -- Dummy blue client for the client.content test
 -- the lua_executable portion may need to get ironed out. I need to specify 5.3
@@ -16,8 +16,9 @@ if lua_executable == nil or lua_executable == "" then
 end
 local client_dim = 250
 local tiny_client_code_template = [[
-local Gtk = require('lgi').Gtk
-local Gdk = require('lgi').Gdk
+local lgi = require('lgi')
+local Gdk = lgi.require('Gdk', '3.0')
+local Gtk = lgi.require('Gtk', '3.0')
 local class = 'client'
 window = Gtk.Window {default_width=%d, default_height=%d, title='title'}
 window:set_wmclass(class, class)

tests/test-spawn.lua

@@ -18,7 +18,7 @@ local exit_yay, exit_snd = nil, nil
 local tiny_client = function(class)
     return { lua_executable, "-e", [[
 local lgi = require 'lgi'
-local Gtk = lgi.require('Gtk')
+local Gtk = lgi.require('Gtk', '3.0')
 local class = ']]..class..[['
 
 Gtk.init()